The present invention relates to a sheet heating device for heating a sheet with a heater while feeding the sheet along a sheet feed path.
Various copying machines employ a drier-type fixing device for fixing a developed image on a sheet of paper or the like with air heated by a heater and applied to the sheet protective member disposed between a sheet feed path and the heater and having a number of small holes for the passage therethrough of heat radiation from the heater. The sheet protective member serves to prevent the sheet from being attracted to or caught by the air blower, or from getting jammed in the sheet feed path.
The proposed sheet protective member is in the form of a metal mesh screen. Therefore, it is necessary to provide a wide insulating gap of 4 mm or more between the heater and the metal mesh screen. The wide insulating gap results in a reduction in the thermal efficiency of the heater.
The metal mesh screen comprises a number of intersecting woven metal wires. The intersecting points of the metal wires however tend to serve as an obstacle to the leading edge of the sheet as it is fed along the sheet feed path. Therefore, the sheet protective member is still ineffective to prevent a sheet jam.
Another proposed metal mesh screen is made up of a number of parallel metal wires extending along the direction in which the sheet is fed through the sheet feed path. The metal wires obstruct the uniform application of hot air from the heater to the sheet. As a result, the sheet is subjected to striped heat irregularities on its surface, so that color irregularities may be caused on the sheet or the sheet may not be calendared uniformly.
The metal mesh screen is fixed to a support frame by screws or welding. However, the sheet protective member of such an arrangement is expensive to construct. There has also been proposed a plate-like sheet protective member having a plurality of slits extending along the sheet feeding direction. However, the sheet as it travels along the sheet feed path tends to be caught by downstream ends of the slits.